The Positive Crankcase Ventilation (PCV) system is used to control and purge the crankcase blow-by vapors. The gases are recycled in the following way:
As the engine is running, clean, filtered air is drawn through the air filter and into the crankcase. As the air passes through the crankcase, it picks up the combustion gases and carries them out of the crankcase, through the PCV valve, and into the induction system. As they enter the intake manifold, they are drawn into the combustion chamber where they are burned.
The most critical component in the system is the PCV valve. This valve controls the amount of gases that are recycled into the combustion chamber. At low engine speeds, the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of gases into the intake manifold. If the PCV valve becomes clogged, the system is designed to allow excessive amounts of blow-by gases to back flow through the crankcase tube into the air cleaner to be consumed by normal combustion.
The Positive Crankcase Ventilation (PCV) system must be operating correctly to provide complete removal of the crankcase vapors. Fresh air is supplied to the crankcase from the air filter, mixed with the internal exhaust gases, passed through the PCV valve and into the intake manifold.
The PCV valve meters the flow at a rate depending upon the manifold vacuum. If the manifold vacuum is high, the PCV restricts the flow to the intake manifold. If abnormal operating conditions occur, excessive amounts of internal exhaust gases back flow through the crankcase vent tube into the air filter to be burned by normal combustion.
Because the PCV valve vents the crankcase, a defective valve allows the build up of harmful blow-by gases that dilute and damage the lubricating properties of the engine oil. Additionally, the crankcase operating pressure increases and may cause a gasket or seal failure, resulting in an engine oil leak. In extreme cases, a seal or gasket could be completely forced away from the sealing surfaces, causing a severe oil leak.
Never operate an engine without a PCV valve or a ventilation system, except as directed by testing procedures, for it can become damaged.
Incorrect operation of the PCV system can cause multiple drivability symptoms.
A plugged valve or hose may cause:
A leaking valve or hose would cause:
- Check the PCV lines and connections for restrictions and leaks.
- Start the engine and allow the engine to reach a warm idle.
- With the engine running at idle, using a suitable pliers or fingers, squeeze the hose between the PCV valve and the intake manifold. The PCV valve should make a clicking noise when the hose is squeezed closed.
If the PCV does not make a clicking noise:
- Shut off the engine, and remove the valve.
- Shake the valve and listen for a rattling noise:
- If the PCV valve doesn't rattle or doesn't move freely when shaken, replace it and recheck the system.
- If the PCV valve does rattle freely when shaken, check the valve's grommet and hoses for leaks and replace any parts that are cracked or damaged. Recheck the PCV valve operation.